Evidence for the localisation of electronic charge in electrochemically reduced copper(I) complexes with electron deficient ligands: a structural and spectroelectrochemical study ‡

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Abstract
The electrochemical and spectral properties of copper(I) complexes with binaphthyridine ligands, bn and tbn (where bn = 2,2′-1,8-binaphthyridine, tbn = 3,3′-trimethylene-2,2′-1,8-binaphthyridine), have been studied. The complexes are [Cu(bn)2]+ 1, [Cu(tbn)2]+ 2, [Cu(bn)(PPh3)2]+ 3 and [Cu(tbn)(PPh3)2]+ 4. Reduction of 1–3 results in the formation of radical anion species involving the ligands. Reduction of 4 results in decomposition. For 3– strong near infrared absorptions (1000 nm) are observed suggesting a bn˙– radical anion species, in which the redox MO extends across the entire ligand. For 2– absorptions at 750 nm suggest a redox MO which is much less extensive and localised on a single naphthyridine unit of the tbn ligand. Reduction of 1 is complicated by the presence of two closely lying reduction waves. Application of a reducing potential resulted in spectral features similar to those observed for 3–. However, further reduction showed spectral features similar to those of 2–. The crystal structure of 3·BF4 was determined by single-crystal X-ray diffraction.

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